The present invention relates to a current-pressure transducer, particularly for a vacuum control in automotive vehicles, having a vacuum chamber divided by a membrane with a double valve on one side of the membrane activatable by pressure on the membrane, and including a solenoid activatable valve on the opposite side of the membrane and connected to the membrane.
Such current-pressure transducers can be used in exhaust gas return systems and in a turbo-charger control for controlling the bypass valves.
Features of current-pressure transducers of this type are known a vacuum regulator for vacuum systems, in particular for the testing of ignition distributors with double vacuum displacement, in which a single vacuum pump and two such vacuum regulators are used (Federal Republic of Germany OS No. 21 09 597). One chamber of this vacuum regulator is provided with a connection for supply vacuum as well as with a connection to receive an adjustable controlled vacuum. The chamber is closed off on one side by a membrane which is connected, via a spring, to a threaded rod which, in its turn, rests via a knurled nut against an extension of the chamber. Depending on the adjustment of the threaded rod, a greater or lesser force is exerted on the membrane. The position of the membrane depends on this force and on the vacuum prevailing in the chamber as compared with the external pressure (atmospheric pressure). Via a double-armed lever, the membrane acts on a first valve member, which is developed as a ball and rests within the chamber against a conical valve seat, and on a second valve member, also developed as a ball, which is arranged outside the chamber. A compression spring urges the second valve member at all times towards the corresponding valve member. The first valve member is moved by the vacuum in the chamber against its valve seat as far as the deflection of the membrane permits. The second valve member then lifts off from its seat and establishes a connection between the chamber and the outer pressure (atmospheric pressure) when the knurled nut is displaced in the direction towards lesser vacuum in the chamber. The second valve member then closes again when the vacuum in the chamber has reached the predetermined value.
It is, to be sure, conceivable to replace the threaded rod, the spring and the knurled nut of the known pressure regulator by an electromagnet with plunger-type armature in order to control the vacuum in the chamber, and thus the available control pressure, as a function of the current with which the said electromagnet is energized. This, however, still does not provide any teaching as to how a pressure-current characteristic of such a current-pressure transducer can be controlled in such a manner that this characteristic becomes steeper or less steep. One could at most think of replacing the spring between the threaded rod and the membrane, but by this only a stepwise adjustment of the characteristic is possible.
The object of the present invention is therefore to develop a current-pressure transducer of the aforementioned type in such a manner that a pressure-current characteristic of adjustable slope can be obtained. The linearity of the pressure-current characteristic should be affected as little as possible thereby.
This object is achieved by the construction of the current-pressure transducer with an approximately annular air slot (6) between the plunger-type armature (5) and a core (3) of the electromagnet (1) developed eccentrically to the longitudinal axis (4) of said electromagnet and rotatably adjustable around the longitudinal axis, and that the plunger-type armature (5) is mounted swingable around the swing point outside the center line.
The inventive principle includes the fact that the narrowest place in the radial air gap is shifted with respect to the point of swing of the plunger-type armature. The narrowest point in the air gap is at the same time the place where the greatest amount of force is present between the plunger-type armature and the core of the plunger-type armature electromagnet. By the displacement of the narrowest point of the air gap, the point of attack of the resultant total force is thus also changed. Since the point of swing is asymmetric to the center line of the system, there is produced around the axis of swing on the plunger-type armature a greater or lesser moment, which acts on the membrane--preferably via the valve block. The eccentric development of the air ga between the plunger-type armature and the core of the electromagnet presupposes a construction of the plunger-type armature electromagnet which is practically of rotational symmetry around the longitudinal axis.
Thus, by the rotary adjustment of the eccentric air gap the slope of the pressure-current characteristic can be changed, the slope depending on the factor by which a current exciting the plunger-type armature electromagnet causes a prestressing of the membrane at the chamber.
By the rotary adjustment of the air gap the linearity of the characteristic, i.e. the dependence of the resultant control pressure on the exciting current is no impaired.
The precision of the current-pressure transducer is not reduced by the adjustment of the characteristic since no additional frictional hysteresis is produced by the setting means for the radial eccentric air gap. Finally, the means for setting the eccentric air gap can be manufactured and mounted at little expense.
In detail, as will be described hereinafter, a leaf spring is provided for the swingable mounting of the plunger-type armature. The restoring force of such a spring is so slight that the pressure-current characteristic is not falsified thereby. A leaf spring represents a simple means for achieving the hinge-like mounting of the plunger-type armature.
The eccentric shaping of the approximately annular air gap is produced in particularly inexpensive manner according to a further feature of the invention by a corresponding shaping of the substantially cylindrical coil core of the plunger-type armature electromagnet. The coil core is rotatably adjustable, i.e. the coil core can be turned manually in order to adjust the pressure-current characteristic, but it then retains its rotary position upon the operation of the current-pressure transducer.
With an additional pretensioning spring, in accordance with another inventive feature, which spring connects the coil core of the plunger-type armature electromagnet to the plunger-type armature and/or the membrane of the chamber, the zero point of the characteristic can be established or offset a desired amount.
By means of a set screw, tee initial tension of the biasing spring is preferably continuously adjustable, so as to be able to continuously displace the zero point of the pressure-current characteristic.
The double valve, which forms part of the current-pressure transducer, is developed, in accordance with to-yet another inventive feature, with a valve block which is formed essentially as a hollow cylinder and is introduced into the membrane. The valve block, in combination with a valve member which is pressed against a knife-shaped atmospheric valve seat, forms an atmospheric valve between the chamber and the outer pressure. Furthermore, it forms a vacuum valve together with a supply valve seat on the connection for supply vacuum. The valve member which cooperates with this valve block can generally be of disk shape. In such case, the central region of the disk serves for the closing off of the supply valve seat while the outer edge of the disk of the preferably circular disk cooperates with the knife-shaped atmospheric valve seat in the valve block. Proper operation, i.e. the possibility of the complete closing at the same time of the atmospheric valve seat and of the supply valve seat, presupposes, however, that the two valve seats lie in planes which are precisely parallel to each other. This requires a corresponding expense in manufacture, and particularly assembly expense.
However, by the special development of the valve member in accordance with a flattered special shell construction, both the supply valve seat and the--simply developed--atmospheric valve seat can be simultaneously closed tight with the same valve member even if the valve seats do not lie in planes which are precisely parallel to each other. The position of the valve member is determined by the supply valve seat, which is tightly closed by the one of the two flattenings of the valve member, which has the shape of a spherical shell. If, in this situation, the atmospheric valve seat is also to be closed by the valve member, this automatically takes place completely as a result of the curvature of the spherical part of the valve member which cooperates with this valve seat. By the dependable closing of the supply valve seat the consumption of air can be minimized, i.e. in the adjusted condition of the current-pressure transducer a source of vacuum is acted on only corresponding to the removal of control pressure. In this way, special possibilities for use are opened up for the current-pressure transducer in automobile construction, particularly in diesel vehicles with limited vacuum pump power. The second of the two flattenings of the valve member contributes essentially to the dependable alignment of the valve body on the supply valve seat when the current-pressure transducer is placed under swinging load, caused, for instance, by engine vibration. Due to the second flattening, the valve member is developed symmetrically to the central plane which lies parallel to the two flattenings. In this way, the center of gravity and center of moments of the valve member practically coincide and the valve member, which rests on a compression spring, does not assume a Preferred position resulting from the center of gravity.